DENVER (Reuters) - Relatives of victims of a Colorado movie theater shooting rampage demanded on Monday that President Barack Obama and Mitt Romney address gun violence in their first presidential debate this week in Denver.

In a letter to debate moderator Jim Lehrer, relatives of eight of the 12 people who died at a midnight screening of “The Dark Knight Rises” in July urged him to ask the men who want to lead the country about mass shootings in Colorado at Wednesday night’s debate.

“To ignore the problem of gun violence where two of the worst shootings in U.S. history took place - Aurora and Columbine - would not only be noticeable by its absence but would slight the memories of our loved ones killed,” the letter said.

James Holmes, a former neuroscience graduate student, has been charged with murder and attempted murder in the July 20 rampage, one of the worst U.S. outbursts of gun violence in recent years. In addition to those killed, 58 people were wounded.

That rampage took place about 15 miles from the scene of a 1999 shooting at Columbine High School, where two students shot dead a teacher and 12 students before committing suicide.

A spokesman for the Public Broadcasting System’s “NewsHour” show that Lehrer hosts said the group’s letter was passed along to him and that Lehrer was en route to Denver for the debate at the University of Denver and not available for comment.

Talk of reining in America’s gun culture is considered politically risky for Obama ahead of the November election. He called for an end to “senseless violence” after the movie theater shootings and another this summer at a Sikh temple in Wisconsin but has been careful not to take a stand on gun control.

Romney has said that additional laws would not have stopped the massacre.

In a separate initiative, a man wounded in the theater shooting, Stephen Barton, appears in a television ad that will air nationally this week in which he asks the candidates to explain how they would reduce gun violence.

“I never thought I’d be a shooting victim until I was bleeding on a floor in Aurora,” Barton said in a statement. “I was lucky, but I’ve seen what happens when dangerous people get their hands on guns. And I think it’s fair to ask the men who want to lead the country to get past the platitudes and give us a serious plan to address a serious problem.”

The ad features Barton sitting in an empty theater explaining how he was shot in the face and neck, adding that 48,000 Americans will be killed by firearms in the next four years unless lawmakers take action.

The ad is sponsored by Mayors Against Illegal Guns, a coalition of 725 U.S. mayors led by Michael Bloomberg of New York and Thomas Menino of Boston that advocates closing loopholes in gun laws to prevent felons, the mentally ill and “other dangerous people” from obtaining firearms.

Bloomberg said in a statement about Barton’s ad: “When the candidates walk into that auditorium, I hope they’ll be thinking about another theater a few miles away where a dozen people were murdered, and dozens more were injured like Stephen.”